Conventional semiconductor transistors are well known in their ability to provide high speed switching capability in a relatively inexpensive and small size. Conventional semiconductor-based transistors do, however, suffer from various problems that are not present in mechanical microswitches. Mechanical switches, moreover, include many promising properties that semiconductor transistors lack. For example, micromechanical switches can be built to have a very high “off” resistance and a low “on” resistance resulting in lower loss and less power dissipation. This feature is particularly advantageous because certain applications (e.g., radio frequency applications) require higher electrical isolation between components. Another advantage offered by mechanical switches is that they are more linear and stable with respect to a wide variety of operating conditions such as voltage, current, temperature, pressure, and radiation.
Various micro-electrical-mechanical (MEMS) switches have been proposed and developed for switching applications. Despite the variations in detailed designs and actuation methods, almost all the MEMS-based microswitches utilize microscale beam structures. These types of microswitches operate with solid-to-solid contact between elements, sharing many typical problems of macroscale mechanical switches such as surface degradation (leading to an increase in the contact resistance) and signal bounce effects during switch actuation.
The use of conductive droplet systems has been proposed to overcome these limitations, liquid metals being the droplet material for most applications. In these systems, a metallic droplet such as mercury is physically moved by typically an electrical actuation toward a contact element in a microswitch. The droplet systems generally offer low contact resistance, linear responses, and long lifetimes. Unfortunately, existing droplet-based microswitches have limited application because of the slower switching speeds. An important aspect of the switching speed is switch latency, referring to the amount of time that elapses between actuation of the switch and the closing of the switch. In the case of droplet microswitches, the closing is effectuated by droplet movement. Consequently, their latency tends to be larger (slower) than that of the solid beam-based micro switches and much slower than that of semiconductor switches. In these metallic droplet systems, the lowest reported latency period is on the order of 1 millisecond. See e.g., W. Shen et al., Electrostatically Actuated Metal-Droplet Microswitches Integrated on CMOS Chip, J. MEMS, Vol. 14, No. 4, August 2006, pp. 879-889. There thus is a need for metal-droplet microswitches that have faster switching rates. For example, switching rates at or below around 100 μs (micro seconds) would enable microswitches to be used in many more applications such as, for instance, RF switches and dynamic displays. Such switches would have high performance characteristics of, for instance, high durability, low resistance, no signal bounce, in addition to the high speed switching capability that has heretofore been unrealized in existing metal-droplet switches.